| 401-1 | Hard core foam in wing instead of balsa wood SN 28 & up | | German | English |
| 401-2 | Airbrakes on lower wing surface omitted, brakes on upper wing surface enlarged, SN 25 and up | | German | English |
| 401-3 | Aileron construction without balsa wood SN 33 and up | | German | English |
| 401-4 | Improved canopy lock SN 22, 23, 24 and 25 | | German | English |
| 401-5 | Tilt-up canopy (center section) with bolt-on GFRP aft section Standard on SN 26 and up | | German | English |
| 401-6 | Installation of wing fuselage fillets Standard on SN 26 and up | | German | English |
| 401-7 | Installation of aileron/flap superimposing linkage Standard on SN 26 and up | | German | English |
| 401-8 | Improved airfoil section for horizontal tailplane, anti-flettner tab, trim spring Standard on SN 28 and up | | German | English |
| 401-9 | Hard core foam instead of balsa wood, Standard on SN 28 and up | | German | English |
| 74-323/2 | 401-10 | Inspection of rudder cabbIes in the area of the S-shaped guides on the rudder pedals, replacement if damage is discovered, all SN | Every 100 hours or annually (whichever comes first) | German | English |
| 401-11/2 | Anti collision markings - various colour Supersedes TN No. 401-11, all SN | Before 1/7/1971 | German | |
| 401-12 | Different glass cloth for shear web: See drawing No. 401-52-5, Note 1 for alterations | | German | |
| 401-13 | Different glass cloth for shear web: See drawing No. 401-52-5, Note 1 for alterations | | German | |
| 401-14 | Reinforced spar stubs and reinforced stub fittings, Standard on SN 101 and up | | German | |
| 401-15 | Modification of the torque tube actuating the airbrakes: Standard on SN 96 and up | | German | English |
| 79-233 | 401-16 | Airbrake actuating system inside the wing: Replacementof the rod ends and control for cracks | Before 15/6/1979 then annually | German | English |
| 81-266 | 401-17 | Increase of the service life limit to 6000 h All SN | Before 3000 hours, 31/3/1982 at latest | German | English |
| 84-266 | 401-18 | Possible damage of wing structure with water ballast bags installed. Revision of flight manual. | Before 1/5/1984 | German | English |
| 86-221 | 401-19 | Rudder-yoke Replacement of the yoke | Before 31/3/1987 | German | English |
| 87-83 | 401-20 | Replacement of "DIN" control cables by "LN" cables | Before 31/7/1987, then every 500 hours | German | English |
| 401-21 | Elevator drive bracket: Possibility of replacement by elevator drive bracket acc. to drawing No. 201-33-4 | | German | English |
| 401-22 | Tow releases: Optional use of model E85 instead of E72/E75 | | German | English |
| 401-23 | Modification to single-piece tilt-up canopy by Glasfaser-Flugzeug- Service | | German | English |
| 96-133 | 401-24 | Inspection of glass fiber laminate on spar stub fitting | Annually | German | English |
| 96-139 | 401-25 | Control surface weight and static balance | Before 31/3/1996 | German | English |
| 02-051 | 401-26 | Possible cracks on airbrakes actuation shaft | Before 31/3/2002 | German | English |
| 401-27 | Replacement of airbrake drive gear inside wing, optional | | German | English |
| 401-28 | Extension of service life limit to 12000 hours, all SN | Before 31/3/2006 and before reaching 6000 hrs | German | English |
| 401-28 | Manual | | German | English |
| 401-29 | Installation of Mode-S-Transponder and Transponder Antennas | | German | English |
| EASA AD 2011-213 | 401-30 | Inspection / replacement of elevator control rod in vertical fin | 30 days, before 31/12/2012 | German | English |
| 401-30 | Authorised service facilities for TN 401-30 | | German | |
| 2018-0143-E | May-18 | Deflector-angles at the C.G. release. Usage of connection ring pair meeting LN 65091 | Annual Inspection | German | English |
| 401-31 | Installation of backrest with integrated headrest | | | English |
